Monitor for multiplex telegraph systems



Feb. 1l, J. l.. FlNcH MONITOR FOR MULTIPLEX TELEGRAPH SYSTEMS 2 Smets-Sheet l AAAA lijlilil (lililili INVENTOR JAA/15st. F/NcH BY M AToRNEY Feb. 1l, 1941. J, L FINC'H 2,2315442 MONITOR Fon MULTIPLEX TELEGRAPH SYSTEMS Filed-April 30, 1937 2 Sheets-Sheet 2 Ime/ABLE wwf/:Emmy 65, asc/11470@ D. C'. SOI/RCE INVENTOR JAMES L. F/NCH ATTORNEY Patented Feb. 11, 194i.

PA'rsN'r orio MONITOR FOR lVI'UL'l'IlLEXv TELEGRAPH SYSTEMS James lL. Finch, Patcliogue, N. Y., assigner to Radio Corporation oi Americara comi-ation of Delaware Application April 30, 1937, Serial No. 139,866

Claims.

This invention relates to a monitor for a time division multiplex telegraph system and more particularly it has to do with a device which hasbeen' found to be serviceable in the supervision of radio 5 telegraph terminal equipment.

In multiplex radiok telegraph systems it is important-that the keying operations be carefully observed in order to determine as promptly as possible any departures of the keying signals from the channel timel allotments of the multiplex system. Present day practice in the operation of multiplex telegraph systems makes it essential that a constant tone frequency and the frequency of signalling mpulsesbe maintained in step. If the time is not equally divided between the different channels of the multiplex system, then failures are apt to occur in the assignment of each signal to its proper channel. Furthermore, the marking and spacing intervals of the code signals become clipped because they do not register with the commutation points.

Accordingly, it is among the Objects of my invention to provide a monitoring indicator wherebythe correct impress of keying signals upon the transmitter shall be clearly indicated as in phase or out of phase with the operation of the commutator which distributes the time allotments to each signaling channel.

In carrying out my invention I have found that the cathode ray tube oscilloscope lends 'itself readily to the indication of operating conditions. The keying of code signals on each of a plurality of multiplexed channels is clearly indicated by the image whichmay be projected on the fluorescent screen of an oscilloscope. The transient keying signals occur so rapidly as to give effect to persistence of vision phenomena so that denite areas of the iiuorescent screen appear to be lightedV up continuously. If these areas appear to move in one direction or another certain indications are thereby given which are helpful to the operator in controlling the operation of the terminal apparatus.

My invention will now be described in detail, reference being made to the accompanying drawings in Awhich Figure 1 represents diagrammatically a circuit arrangement of a preferred embodiment, and

Fig. -2 shows a modified circuit arrangement.

With reference to either of the embodiments illustratively used in the following description, it may be said that essentially there is required a suitable power supply unit, a very low frequency oscillator, a phase differentiating device for maintaining a 90 phase difference between voltages impressed upon the horizontal and vertical deiiecting circuits respectively in a cathode ray tube oscilloscope, and finally an amplification stage on which input signals may be impressed and thence delivered to suitable control circuits of the oscilloscope, whereby indications may be made on the fluorescent screen.

Referring first to Fig. 1, there is shown a power supply unit which comprises a transformer I for obtaining a suitable voltage from any available commercial alternating current, say, of 60 cycle frequency. The secondary 2 of the transformer feeds energy to a duplex diode tube 3. This tube acts as a voltage doubler. One side of the secondary is electrostatically grounded through the conl5 denser 4 and is provided with a return circuit through a capacitor .i to the cathode 6 of the tube 3. The anode l and the cathode 8 are interconnected, while the anode 9 is grounded.

Rectiied current is taken off from the cathode 6 and from the capacitor 5 and its ripple component is smoothed out by means of suitable chokes III and II. A grounded by-pass condenser I3 is preferably connected to a point intermediate the chokes I0 and II. 25

.v The low frequency oscillator unit comprises an electron discharge tube I4 preferably of the pentode type. having its anode I5 connected through a conventional Hartley oscillator circuit to the D. C. source described in the preceding paragraphs. This circuit includes a variably reactive transformer I6, the primary of which has an intermediate tap I1 in circuit with a connection between the ilter chokes I0 and II. A

screen grid potential is also derived from the filter system and fed through the resistor I8 to the screen grid I9. The two transformer primary terminals are intercoupled through the tuning condenser 20 thereby forming a resonant circuit which is tunable to the low frequency required for suitable operation of the oscilloscope deflector circuits. In the exemplary embodiment under discussion frequencies from 14 to 23 cycles per second are contemplated although other frequencies may, of course, be obtained, if required.

Energy is fed back from a suitable point on the resonant circuit I1-20 through a capacitor 2l to the control grid 23. 'I'he control grid 23 has a relatively low impedance path to ground through the resistors 22 and 24. The cathode 25 is also 50 grounded through a suitable resistor 26, the ohmic value of whichis considerably higher than that of 'the combined resistors 22 and 24.4 The capacitor 21 serves as an ordinary alternating current path from the screen grid I9 to the cathode 55 25. l Any variation in cathode .voltage with respect to ground is also impressed on the grid leak 24 through condenser 21m-'and thus prevents de- `generative eiects whichfmight otherwise be present if the energy were inadequately by-passed through the resistor V26.

vtribe oscilloscope 3|; The plates so connected are ing plates 35. A capacitor 36 havingA an approxl- The secondary winding .28ct the transformer i5. delivers oscillations lto the ,'windinfgsii and oftwo transformers whose functionl will pr'es-A opposed to companion plates which are grounded.

The voltage 'generated in the winding 2B is impressed across a resistor 32 and a capacitor 33,'th'e respective values of which are preferably of thev .order ofj 1000 ohms and 4 microiarads. Two

voltages are thus obtained with a- 90 phase difierence therebetween. One of these voltages is fed toward the r-horizontal deilectirig plates 34, while the other voltage is fed toward the vertical deilectmate value of .25 microrarad serves to, adjust this circuit so as to obtain exactly 9 0" oi "phase displacement with respect to the voltage in the-vertical deilecting circuit. Each oi the amplifiers and 51 is provided with an adjustable gain-control deviceso that the amplitudes of horizontal and vertical deection of thel cathode ray maybe equalized, thereby to produce normally an image o fcircular pattern.. Si Voltages from the keying circuits f the multiimposedupon the oscillator output. voltagesby "l means of the transtormers'whose windings 29 and yill) have already been mentioned. These transformers possess primary windings 31 and-3,8 respectively.- These primaries, however, are excited by potentials which are substantially in 90 phase relation to one another,- although both voltages are derived fromthe output circuit of an ampliier tube 39 which yis preferably of the pentode and thence through a by-pass condenser 4'6 .tothe anode 41. .A positive D. C. potential is applied to the anode 41 from the power supply unit and?" through the reactor l2. A grounded capacitor 52 aids.in dissipating any ripple component in the power supply. Positive potentialior the screen grid 53 is obtained from the. power Supply unit 'through the resistor 54. .The screen 'grid 53 may be electrostatically grounded through the capacitor 55 and resistor` 44.;

A phase displacement between the voltages tained by virtue of a resistor '48 across the terminals of .the winding 31 and a capacitor 49 across the terminals of the winding 38. This phase displacement` results in circular' deilection ofthe oscilloscope spot responsive to the Signal frequencies in amanner similar to that produced by the low frequency oscillator.

Part of the signal input energy may be used to control a phase corrector. whereby the'drlving motor 8l is held in synchronism with`the incorning signals.' The motor 8l drives a channel time The signal input is preferably/,jed through a transformer 4 0 and thence it is, i'nipressed'upon` the control grid 4l. This grid issui'tably biased by means of resistors 42, 43 and 44 forming a distributor 92 in accordance-with Well known practice. In the absence of signals the path traced bythe electron beam causes 3a pattern of substantially circular shape to be imaged non theiluorescent.

screen of the oscilloscope 3l'. This is -due'toftlie rotary control of the deecti'ng circuits by the' esemater. when, however, impulses are derived from the signalling circuit these additional voltages are superimposed upon the-oscillator voltages Y that if the-voltages were to be derived from a con- .tinuous signal tonefrequencyalone the oscilloscope `circle would be much smaller than when produced by the output of f theoscillator alone.

. vLet it now be assumed that the signals to be monitored are derived from two multiplex channels and that thecommutator'i'requencyissubstantially 22 vcycles persecond., The frequencyof the oscillator will alsobe' set tof22 cycles. Let it now .be assumed that." on both channels a tone keying with a series of dots is'enective. At the instant when the oscilloscope spot'is-at the highest point of its circle channel -A may have just been A 1 will .maintainxcontrol 'while ythespOt travelsfrom that point through an arcrof to the extreme right point on the circle. Channel B will then take controll'for the next 90 of. travel. plex telegraphsystem to be monitored are superperiods the transmitter will be'fin the spacing condition. Thus, while the spotis traveling from the extreme upper position through are to the lower position, the tone signal should b e on. For the remaining 180 it should be oil. "When the tone signal. is on it causes a superimposed circular deection o'f they spot and thustraces what appears to be. a.A helicalline centered about .the circle which it traces ywhen the signal is oi.

When miscellaneous characters'yof the Morse code are being transmitted by one or both chanlnels then the various quadrants of the circle will have marking characters. forpart ofthe time.I

However, these characters -willf-.always start and it the variabletap 59 on the potentiometer 42 so stop 'at the ends of the quadrants. Itthe signal `is properly balanced, then. these points. where starts and stops are made Iwill be tru1y90 apart.

If. however, the lengthv of timeaSSEDed to the4 various channelsis incorrect, then these starting and stopping points will not 'b e 901 apart and that fact can be noted by means ofthe indications made on the oscilloscope screen. across the windings 31 and 38 respectively isopaction 'of the pattern traced by the spot'on the cathode ray tube screen. In case lthere is interference of any kind onthe radio circuit this wouldbe' superimposed on the signal and can vbe noted-by miscellaneous deviations o! the trace from the picture which would normally be expected. Likewise any breaks in the characters can easily be-seen. 4

I-have assumed that the signal input is a given control er. the transmitter. 'Then channel $0 tone signal for purposes of description. It will also be possible to impress on this monitor picture, transient currents corresponding to the start and stop of marking characters on the transmitter. This could be obtained by feeding the output of a radio frequency monitor rectier to the input terminals. Thus, while the transmitter was either on marking or spacing, a steady current would flow through the input transformer winding and no deflection would be caused from this source. At the start and stop of characters this current would change and cause a transient deflection of the spot. In some cases this type of input signal may be found preferable to that of a tone signal.

Referring now to Fig. 2, I show a modified form of the invention in which the oscilloscope comprises a cathode ray tube 60 having a control grid 6| in addition to'the usual electrodes as shown in the tube 3| of Fig. 1. The signal input to be monitored is fed through the amplifier 62 and across the capacitor 63 to the control grid 6|.

A direct current power supply unit 64 furnishes the necessary operating potentials to the cathode ray tube 60, and to the amplifier 62. This same unit 64 may also be used to supply power to the variable low frequency oscillator 65, and to the amplifiers 56 and 51, although the connections thereto are not shown, due to the fact that these portions of the system may be of conventional design and Fig. 2 is largely a block diagram.

A potentiometer 66 is grounded at onepoint so that the negative terminal may connect through a reactor 61 to the control grid 6|,

thereby to bias the same strongly `negative with respect to the grounded cathode 68.

Anode potential is fed directly from the source 64 to the anode '69 nearest the fluorescent screen of the cathode ray tube. A lesser positive voltage is derived from a tap on the potentiometer 66 and fed to the focussing anode 1|). Any suitable anode potential may be taken Ao the potentiometer 66 and fed through a reactor 1| to the anode or anodes of tubes (not shown) in the amplifier 62.

The oscillator 65 functions in thesame manner as the oscillator of Fig. 1. The output energy is fed partly through a resistor 12 to the amplifier 56 and partly through a phase adrluster unit 13 and a variable capacitor I4 to the amplifier 51. The ampliiiers 56 and 51 are each provided with gain controls so that their output voltages may be equalized at any operating frequency. l

In the operation of the system shown in Fig. 2 a circular path is traced by the spot on the oscilloscope screen due to the phase difference between the potentials applied to the horizontal deflecting plates 3H and the Vertical deilecting plates 35, respectively, these potentials being derived, as has ibeen explained, from the low frequency oscillator 65. impulses from the keying source, however, are fed through the amplifier 62 to the control grid 6| of'the cathode ray tube. This grid is negatively biased to such an extent that the electron beam is blocked, say for spacing signals, and reaches the fluorescent screen only during marking signals. Different arcs of the circular path on the screen are, therefore, illuminated. The allotment of time to the marking signals of different channels can thus be compared by noting whether the illuminated arcs are longer or shorter than they should be for equalization of the channel time.

While I have coniined the foregoing description substantially to two specific embodiments of the invention, it will be understood by those skilled in the art that various modications may readily be made without departing from the spirit and scope of the invention itself.

I claim: V

1. A monitor device for synchronous telegraph keying systems, comprising an electron discharge tube oscillator, a source of keying signals, a channel time unit distributor with which said keying signals are intended to be maintained in synchronism, means for adjusting the frequency of said oscillator to a value having substantially a sub-harmonic relation to the channel time unit frequency, a cathode ray tube oscilloscope having horizontal and vertical beam deiiecting means, means for deriving from said oscillator potentials which have a 90 phase dierence therebetween, means under control of said keying signals for splitting the impulses thereof into two voltages having a 90 phase difference, and means for superimposing each of the last mentioned voltages respectively on different voltages derived from the oscillator and for impressing the same respectively on the horizontal and on the vertical beam deiiecting means thereby to produce an oscilloscope image having traces of concentric arcs whose subtended angles are indicative of the conditions to be monitored.

2. A device in accordance with claim 1 and lhaving means including capacitive and resistive elements for producing the phase differentiated voltages which are respectivelyapplied to the horizontal and vertical deilecting means.

3. An indicator for use in multiplex code signal keying systems, comprising a cathode ray oscilloscope having horizontal and vertical beam deiiectors, a variable low frequency oscillator, means including a phase-splitting device for feeding energy from said oscillator to each of said deiiectors, the potentials of said energy as fed to the different deflectors having a quadrature phase relationship to each other, and means for similarly splitting the phases of potentials -derived from a. code signal source and superimposing the llast said potentials respectively on the oscillator potentials, thereby to produce an image pattern on the oscilloscope screen which image pattern is of differentiated radii and is indicative of the timing of impulses from said code signal source with respect to the potentials of a given synchronizing tone frequency.

4. In the operation of a synchronous multiplex telegraph transmitter having a monitoring device which includesv an oscilloscope, and a low frequency oscillator, the method of indicating agreement with or departure from a given synchronizing frequency in respect to the timing of multiplex code signals, which comprises adjusting said oscillator to a frequency having an aliquot relationsh'ip to said synchronizing frequency, combining signal energy with the output energy from said oscillator, splitting the combined energy into quadrature phase differentiated potentials and causing the cathode ray of said oscilloscope to be deected in rotary paths under control of said phase differentiated potentials, saidpaths being substantially restricted to arcs of two distinct and predetermined radii.

5. A monitor system for indicating a synchronous relationship between the alternating current output from an oscillator and the rhythmic irnpress of signal code elements on a telegraph circuit, said system comprising a cathode ray tube oscilloscope having horizontal and vertical deecting circuits, a. potential phase-splitting device under control of output energy from said oscillator a operable upon said deflecting circuits to pfrieice a rotary scanning action of the electr0n\bea'm in said oscilloscopel a second phasesplitting device coupled to said telegraph circuit,

means for kfeeding potentials of one phase fromV said second phase-splitting device to one of said deecting circuits, and means for feeding poten- 

